1. Field of Invention
This invention relates to systems and methods for generating color images.
2. Description of Related Art
In electrophotographic printing, a photoconductive surface is charged and is then selectively exposed to image data to selectively discharge portions of the charged photoconductive surface. This forms a latent electrostatic image on the photoconductive surface. Charged toner material is then applied to the latent image bearing portion of the photoconductive surface to convert the latent electrostatic image into a developed image. Finally, the developed, or toner, image is transferred to a sheet of recording material, such as paper, by charging the backside of the paper to attract the toner of the developed image from the photoconductive surface to the paper. The developed, or toner, image is then at least semi-permanently fixed to the sheet of recording material, such as, for example, by heating a thermoplastic toner material to fuse it to the sheet of recording material. An example of this process is more fully described in U.S. Pat. No. 2,297,691.
In full color image-on-image systems, this process is repeated a number of times to build a multilayer full-color image. In the image-on-image technique, a first latent image is developed onto a portion of the photoconductive surface. Subsequent latent images are exposed through the first image, on the same portion of the photoconductive surface, and then developed.
In image-on-image systems, different color features of an input image are formed at separate print stations of the image forming device. Therefore, each print station is responsible for processing one of a number of different colors, such as, for example, magenta, yellow, cyan or black. Each print station typically contains three substation components: a charging substation, an exposing substation, and a developing substation. These stations and their substations are arranged serially around the photoconductive surface. Thus, in such image forming devices, the photoconductive surface is often a photoreceptor belt. The photoreceptor belt moves past these different substations at a speed that allows adequate time for: (1) uniform charging of the photoconductive surface, (2) sufficient exposure of the latent image, and (3) sufficient developing of the image.
Commercial demands require that these devices operate reliably and that any downtime associated with maintaining the device be minimized. In particular, color non-uniformity, or more formally the within-page color variation, is a key performance attribute which nearly every customer lists as critical for their printing business. Within-page color non-uniformity is the variation that occurs within a given cut sheet size image and is typically due to within-page density variations in the form of streaks and bands. Sources of the within-page color variations are numerous, and can be caused by the charging substations, the exposing substations, the developer substation, the photoreceptor belt module, and/or the transfer substation.